1. Field of the Invention
This invention relates to a process for agglomerating coal particles and simultaneously removing ashes therefrom. More particularly, it relates to such process comprising adding an oil fraction to an aqueous slurry of coal particles or coal fines.
2. Description of the Prior Art
In view of the recent increase in the price of petroleum fuel oils as well as the limited amount of crude oil reserves, much attention is now focused on coal, which is now less expensive and exists in large quantities all over the world. However, one drawback is that coal is rich in substances inert to reactions (including combustion) or rather detrimental to the same, such as inorganic materials (also called ash) including clays, and moisture. Preliminary removal of the ash and moisture in coal dressing plants will bring advantages such as reduction in coal transportation costs, simplification of combustion furnaces, smoke-eliminating apparatuses and the like in thermoelectric power stations, for instance, and fewer problems caused by ash treatment. Therefore, techniques of the so-called coal cleaning, which includes ash removal, desulfurization (with respect to inorganic sulfur) and dehydration are now under active development. Thus, for example, a process has been studied which comprises adding an oil fraction as a binder to a coal slurry to cause agglomeration of coal particles and thereby recover coal agglomerates separately from ash, inorganic sulfur, water and other impurities. However, a study of this process for coal agglomeration in water has revealed a number of problems. For example, the amount of the oil fraction as a binder in agglomeration is too large; the energy consumption in the agglomeration, which can be expressed by the formula n.sup.3 t where n is the number of revolutions per unit time in agitation and t is the agglomeration time, is too large; the process is too expensive from a commercial viewpoint; and ash cannot be removed to a satisfactory extent. Thus, the process cannot be a satisfactory coal cleaning process.
Another process has been proposed, which comprises adding an aqueous emulsion of an oil fraction to an aqueous slurry of coal fines and agitating the mixture to form agglomerates of coal particles. However, this process has a problem of reduced producitivity because preliminary preparation of the aqueous emulsion of an oil fraction is necessary and because it is required to repeat the treatment at least two times.